Tire having two-ply carcass merging into one ply

ABSTRACT

A tire carcass is formed of a pair of plies adjacent to each other and extending through the tire from one bead to the other. Each ply comprises cords arranged with the same pitch and along the same direction, and the cords of each ply are staggered with respect to those of the other by half the pitch. The cords of the two plies, in regions of the carcass close to the beads, are located respectively at different distances from the inner wall of the tire. Successive cords of each ply, in regions of the carcass between the midheights of the two sidewalls, are inserted between adjacent cords of the other ply, so that the cords of the two plies, in regions of the carcass between the midheights of the two sidewalls, are located substantially at the same distance from the inner wall of the tire.

United States Patent [191 de Zarauz TIRE HAVING TWO-PLY CARCASS MERGINGINTO ONE PLY [75] Inventor: Yves Jacques de Zarauz, Le Cendre,

France [73] Assignee: Compagnie Generale Des Etablissements Michelin,raison Sociale Michelin & Cie, Clermont-Ferrand, France 22 Filed: Apr.26, 1972 21 Appl.No.: 247,780

[30] Foreign Application Priority Data Primary ExaminerGerald M.Forlenza Assistant Examiner-Robert Saifer Attorney-Granville M.Brumbaugh et al.

[ 5 7 ABSTRACT A tire carcass is formed of a pair of plies adjacent toeach other and extending through the tire from one bead to the other.Each ply comprises cords arranged with the same pitch and along the samedirection, and the cords of each ply are staggered with respect to thoseof the other by half the pitch. The cords of the two plies, in regionsof the carcass close to the beads, are located respectively at differentdistances from the inner wall of the tire. Successive cords of each ply,in regions of the carcass between the midheights of the two sidewalls,are inserted between adjacent cords of the other ply, so that the cordsof the two plies, in regions of the carcass between the midheights ofthe two sidewalls, are located substantially at the same distance fromthe inner wall of the tire.

7 Claims, 8 Drawing-Figures PATENTEI] JAN 81974 SHEET 2 UF 2 TIRE HAVINGTWO-PLY CARCASS MERGING INTO ONE PLY BACKGROUND OF THE INVENTION Thisinvention relates to tires of which the carcass has a novel and highlyeffective arrangement of reinforcing cords. It relates especially, butnot exclusively, to radial-carcass tires and/or to tires having acarcass reinforced with metal cords. It concerns on the one hand thetires themselves and on the other hand a method of manufacturing thetires.

As those skilled in the art know, the manufacture of a tire entailsinitially the building of a cylindrical blank, which may be formed ofthe carcass only or which may already combine all the structural partsof the tire. During a second stage, the cylindrical blank is shaped andassumes a substantially toroidal shape. As a result of the shaping, thecords of each carcass ply, which are parallel and equally spaced in thecylindrical blank, move away from each other, retaining their initialspacing at the height of the bead wires and becoming spaced farther andfarther apart as they approach the crown of the carcass. In the case ofa radial carcass, the cords, remaining in the radial planes, have theirspacing or pitch increased proportionally to their distance from theaxis of the tire.

The shaping thus has the effect of stretching the bridge of rubberconnecting two adjacent cords of one and the same ply. The width of thisbridge of rubber, which is uniform in the cylindrical blank, isincreased considerably in the finished tire between the bead and theshoulder. An elementary calculation shows that, in a radial-carcasstire, the width of the bridge of rubber varies between a minimum s atthe height of the bead wires and a maximum a at the height of the crown,such that:

d being the diameter of the cords and r the shaping ratio, that is tosay, the ratio of the maximum diameter of the carcass, measured at theintersection with the mid-plane of the tire, and the minimum diameter ofthe carcass, measured at the base of the beads.

The maximum width 6, is a multiple of the minimum width 6,, their ratiobeing, for instance, included between and 30. In certain cases, 6, mayassume a rather large value. Thus in tires for construction equipment,one may have a cord diameter d of the order of 3 mm, a shaping ratio 1'greater than or equal to 2, a minimum bridge of rubber e, of the orderof 0.4 mm, and therefore a maximum bridge of rubbers, of the order of 4mm, namely ten times larger than s It is undesirable for the rubberbridges between adjacent cords to stretch excessively, as this has theeffect of accentuating the heterogeneity of the carcass. This is all themore undesirable when the wider bridges of rubber are located in theupper zones of the sides of the tire, which zones are subject to thegreatest deformations and therefore the greatest stresses. These zonesare therefore less reinforced even though they are more exposed andsubjected to stress. In order to avoid overloading and excessivewidening of the bridges of rubber, two remedies are suggested by formula1 set forth above.

A first remedy consists in reducing as 'much as possible the minimumspace i between cords so as to limit the maximum space 6,. In otherwords, for the building of the carcass one selects plies of which thecords have a pitch, that is to say, a center-to-center distance, whichis as small as possible. This method, however, has only limitedpossibilities. It is obvious that one cannot reduce the pitch and thewidth of the bridge of rubber beyond a minimum value for each type ofcord. In the above numerical example it is difficult to reduce theminimum bridge of rubber between cords of 3 mm diameter beyond 0.4 mm or0.3 mm. Assuming that one succeeds in reaching 01 mm, the maximum bridgeof rubber e, will be reduced only by about 0.2 mm.

Another remedy consists in using cords of smaller diameter, distributedin several carcass plies. Formula 1 shows that, if, instead of a singlecarcass ply of cords of diameter d with a minimum space of s one employstwo equivalent plies of cords of diameter d 1] 2/2 spaced apart adistance J 2/2, the maximum bridge of rubber will thus be reduced to e,1/ 2/2 and will therefore be decreased by about 30 percent.

However, this remedy, while advantageous in theory, proves unacceptablein practice, particularly in the case of metal cords or cords ofmaterial of a high modulus of elasticity. Experience shows that acombination of two superimposed plies whose cords are parallel andhighly resistant to tension and compression forms a sort of very rigidbeam which is much more rigid than a single ply of thicker cords or thana group of plies the cords of which intersect. Accordingly, if on theone hand one decreases the stresses on the bridges of rubber by the useof heavier cords, on the other hand one increases those stresses by theuse of several plies of parallel superimposed cords on which the samedefor mation is imposed.

SUMMARY OF THE INVENTION An object of the invention is to remedy thedeficiencies of the prior art noted above. In particular, an object ofthe invention is to reduce the maximum width of the bridges of rubberbetween adjacent carcass cords without thereby producing a harmfulstiffening of the sidewalls, particularly in the regions adjacent to thetread where they are subjected to strong deformations and strongstresses. Another object of the invention is to obtain this resultwithout having to modify in an undesirable way the ordinary tirebuilding operations.

The foregoing and other objects are attained in accordance with theinvention by the provision of a tire having a carcass formed of at leastone pair of adjacent plies extending fromone bead to the other andformed of cords arranged with the same pitch and with the sameorientation. The tire is characterized in that the cords of the pair ofplies are staggered half a pitch from one ply to the next. Within theregions of the carcass close to the beads, the cords of the two pliesare respectively arranged at different distances from the inner wall ofthe tire. In the region of the carcass between the middle of the twosidewalls, successive cords of one ply are inserted between adjacentcords of the other ply, and the cords of both plies are substantially atthe same distance from the inner wall of the tire.

The pitch of the cords of a ply is the distance between adjacent cordsmeasured from center to center. The pitch is equal to the sum of thediameter of one of the cords and the distance between adjacent cords,that is to say, the width of the bridge of rubber.

The invention thus comprises two plies of parallel cords arranged insuch a manner that each cord of one ply is at an equal distance from twocords of the other ply. The cords of the two plies are superimposed inthe sidewalls in the zones adjacent to the beads but are juxtaposed asthough they were part of a single ply in the regions of the sidewallsadjacent to the tread and below the tread.

The insertion of the two plies one within the other makes it possible toavoid both a stiffening by superimposition of layers of parallel cordsand a widening of the bridges of rubber, particularly in the regionswhere this stiffening and widening are harmful.

The invention is preferably applied to a tire having a radial carcassand/or a carcass reinforced with cords of material of high modulus ofelasticity and in particular metal cords.

Calculation shows that, for a radial tire in accordance with theinvention, the maximum width a of the bridge of rubber between carcasscords at the height of the intersection with the middle plane is givenby the formula:

6, r s /2 +d/2 (1' 2) In this formula 6 designates the maximum width ofthe bridges of rubber between cords of the ply resulting from themerging of the two plies and 5,, the minimum distance apart of the cordsof one and the same layer.

It can be observed that for 'r 2, formula 2 reduces to e, 6 Accordingly,in general, for all tires having an ordinary meridian cross section,that is to say, a shaping ratio equal to or only slightly different from2, the bridge of rubber between adjacent cords of the carcass issubstantially the same at the shoulder and the crown as at the beadwires, whatever the diameter of the cords.

In accordance with the invention, e and e, are preferably close to halfthe diameter of the cords and in any event between one-fourth andthree-quarters of the diameter of the cords.

The method in accordance with the invention for the manufacture of atire by forming a cylindrical blank and subsequently shaping it ischaracterized in that, in order to build the cylindrical blank, there isused at least one ply formed of two super-imposed layers of cords havingthe same orientation and the same pitch e. The cords of one layer arestaggered by half a pitch from those of the other layer, and the pitch eis between 2d and 4d/1 l, d being the diameter of the cords and 'r theshaping ratio of the carcass.

In preferred embodiments of the invention, the cords are of metal, and asingle composite ply is employed, the cords of which are arrangedparallel to the axis of the cylindrical blank. The pitch e is close to3d/2 and is between 5d/4 and 7d/4 for ordinary shaping ratios.

It is important to assure the relative positioning of the carcass cordshaving the same orientation not merely during the stage of the buildingof the carcass or of the cylindrical blank but also at the stage of theforming of the plies. This leads to the production of composite plieshaving two layers of parallel cords staggered half a pitch from onelayer to the other.

and crossing of cords belonging to the two plies. This precision cannotbe obtained since one cannot prevent deformations of the plies duringtheir manufacture, handling and positioning, and there is no reason forthe deformations of one ply to beidentical to those of another ply, orfor there to be a superpositioning of identical irregularities inmanufacture upon positioning. The width of a ply intended for themanufacture of a carcass is about 800 to lOOO times the diameterof itscords. In order to avoid any overlapping and crossing of wires upon thesuperimposing of two plies, there is therefore required a precision ofparallelism of the cords of the order of one-sixth of a degree.

On the other hand, when the relative positioning of the cords of thecarcass is effected during the construction of a composition ply havingtwo layers of cords, it is easy to retain this relative positioningsubsequently, since the two layers undergo the same accidentaldeformations during handling and positioning.

In accordance with the invention, the pitch e of the cords of the twolayers of the composite ply is selected as a function of the height atwhich it is desired that these two layers of cords merge in the finishedtire. For a shaping ratio 1' close to 2, the pitch must be equal to 4d/3if one desires the spacing between cords of the same layer to be equalto the diameter of the cords d at the midheight of the sidewall, and themerging of the two layers of cables to start at this height. With apitch close to 3d/2, the merging commences at one-third the height ofthe carcass.

A composite ply with two layers of parallel cables staggered from onelayer to the other by half a pitch can be obtained by any suitablemeans. For example, one can use calenders of a type customary for themaking of plies. One can also proceed by winding around a cylinder. Forthis purpose a first skim of rubber is placed on the cylinder, and then,by the helicoidal winding of a cord, a first layer of cords with a pitche; a second skim is then applied, and then, by the helicoidal winding ofa cord, a second layer of cords with pitch e staggered with respect tothe first by e/2; finally a third skim is applied. It is easy to obtaina precise staggering of the cords of the two layers if one takes careproperly to take up the play of the guide members. It is then sufficientto cut out the sleeve obtained along generatrices of the drum in orderto obtain lengths of composite ply with two layers of staggered andparallel cords which can be used to build carcasses by placing them on atire building drum with their cords oriented parallel to the axis of thedrum. The relative arrangement of the cords does not change during thehandling.

One advantage of the invention is that, because of the use of compositeplies, it makes it possible to manufacture tires of very largedimensions which can withstand very high loads. With the technique ofthe single-ply radial carcass, it is necessary in order to pass from onesize tire to a larger size to use thicker cords, which gives rise tolarger and larger bridges of rubber in the sensitive zones. A radialcarcass with a composite ply in accordance with the invention, althoughformed of cords of smaller diameter, can present a greater resistanceper centimeter and smaller bridges of rubber than a carcass of the samesize formed of a ply with a single layer of cords.

BRIEF DESCRIPTION OF THE DRAWING An understanding of other aspects ofthe invention can be gained from a consideration of the followingdetailed description of the preferred embodiments thereof, inconjunction with the appended figures of the drawings, wherein:

FIG. 1 is a view in radial section of a tire in accordance with theinvention;

FIG. 2 is a fragmentary view in side elevation of the carcass of thetire of FIG. 1;

FIGS. 3, 4, 5 and 6 are sectional views on a larger scale of the tire ofFIG. 1 along the lines 33, 4-4, 5-5, and 66 of FIG. 1;

FIG. 7 is a sectional view on the same scale as FIGS. 3 to 6 of acomposite ply used to construct the carcass of the tire shown in FIGS. 1to 6; and

FIG. 8 is an elevational view, on a reduced scale, showing the compositeplay of FIG. 7 on a cylinder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a tire 10 inaccordance with the invention.

The carcass is distinguished in that it comprises two plies of cords 1 Iand 12 arranged in radial planes of the tire, as shown in FIG. 2. Thecarcass is anchored at its ends around two bead wires 13 located in thebeads 14. It extends into the sidewalls 15 and below the treadreinforcement 17 composed of five superimposed plies of metal cordswhich stiffen the tread 18. FIG. 1 illustrates the definition of theshaping ratio of the carcass, this ratio being equal to Rs/Rp.

As can be noted from the sectional views of FIGS. 3 to 6, the cords ofthe ply I I and those of the ply 12 are substantially at the samedistance from the inner wall 20 of the tire in the region of the carcasswhich is remote from the bead wires 13 (FIGS. 5 and 6) and are atdefinitely different distances therefrom in the vicinity of the beadwires 13 (FIGS. 3 and 4). On the other hand, at all points of thecarcass, each cord of the ply 11 is equidistant from the two closestcords located in the ply 12.

In FIG. 7 there is shown in section the composite ply with two layers ofcords l1 and 12 as it is before positioning and as it is in the tire atthe height of the bead wires 13. In addition to the layers of cords l1and 12, it comprises three layers of rubber 24, 25, 26, the intermediatelayer being thinner than the other two.

In FIGS. 3 to 7 there have been indicated the values of the pitch e andof the rubber bridges e at the different heights, for the case of ashaping ratio of 2.

FIG. 8 shows how one can obtain a composite ply with two layers of cords11 and 12 with pitch e in each layer, staggered half a pitch e/2 fromone layer to the other.

There can be noted a cylinder which can be rotated around its axis by adrive system known per se and not shown in the drawing. There can alsobe noted a lead screw 31 on which a positioning pulley 32 slides. Thepulley 32 can move at a speed which is strictly proportional to thespeed of rotation of the cylinder 30. A cord 33 corresponding to thecord 11 of FIGS. 1 to 7 has been positioned as a helix around thecylinder 30 which was previously covered with a thin layer of rubber 34over substantially the entire length of the cylinder. After thepositioning and rolling of a very thin separating gum layer 35 in orderto cause it to penetrate properly between the turns of the cord 33, thepulley 32 positions a second cord 36 corresponding to the cord 12 ofFIGS. 1 to 7 wound in a helix with the same pitch as the cord 33. Beforestarting the laying of the cord 36, the position of the pulley 32 hasbeen precisely adjusted to take up the laying play and obtain a secondlayer staggered by half a pitch from the helical winding of the cord 33.A last thin layer of rubber (not shown) is placed on the second cordlayer 36. The composite ply is then cut along a generatrix 37 to obtaina ply whose cords are perpendicular to the edges, the length of which isequal to that of the cylinder 30 and the width of which is equaL to thecircumference of the cross section of the cylinder 30.

Certain advantages of the invention appear from the following table,which compares two radial-carcass tires in accordance with the inventionwith a conventional radial-carcass tire.

Radial, com- Radial, Radial, composite ply conventional posite ply No. Iply No. 2

Cord used:

a. core 3+9 wires of 3+9 wires of 3+9 wires of 0.26 mm 0.30 mm 0.30 mmb. surrounding 9 strands of 8 strands of 8 strands of 3 wires of l+9wires of 1+9 wires of 0.26 mm 0.26 mm 0.26 mm c. diameter 2.4 mm 3.1 mm3.! mm

d. material steel steel steel e. strength 520 kg 1000 kg 1000 kg Layingpitch in each layer 3.6 mm 3.5 mm 4.6 mm

Resistance per centimeter of carcass 2850 kg 2850 kg 4350 kg Maximumbridge of rubber (for a shaping ratio of 2) L2 mm 3.9 mm 1.5 mm

As can be seen, the radial tire with composite ply No. 1 has a carcasswhich has the same strength per cm as the conventional radial-carcasstire. However, it uses cords which are definitely smaller and which areconnected at the shoulder by rubber bridges which are three timessmaller.

On the other hand, the radial tire with composite ply No. 2 employs thesame cord as the conventional radial-carcass tire. The strength of thecarcass is increased by more than 50 percent, while the rubber bridgesin the vicinity of the tread have a width which is more than one-halfless.

The advantages of the invention are considerable. They will be all themore evident when the cord used in the conventional radial-carcass tireemployed in the above comparison is the largest metal cord at presentused in tires (of a size of 37.5 X 39): by using the same cord one canincrease the strength of a carcass by 50 percent and thus have a carcasswhich can be used in tires of larger size and.capable of withstandingvery much larger loads. It goes without saying that the in vention isnot limited to the case of giant tires, and that it also makes possiblebetter utilization and greater efficiency of the carcasses of tires ofsmaller dimensions.

Thus there is provided in accordance with the invention a novel andhighly efiective tire and method of its manufacture. Many modificationsof the representative embodiments disclosed herein will occur to thoseskilled in the art. For example, a composite ply can be formed with twolayers of cords which differ from one layer to the other but which arearranged with the same pitch and staggered by half a pitch from onelayer to the other. Accordingly, the invention is to be construed asincluding all the embodiments thereof that are within the scope of theappended claims' I claim:

1. A tire comprising an annular tread portion, a pair of sidewallsrespectively extending radially inwardly from opposite edges of thetread portion, a pair of shoulders respectively at the junctions of thetread portion and the sidewalls, a pair of beads respectively at theradially inner edges of the sidewalls, and a carcass formed-of at leastone pair of plies adjacent to each other and extending through the tirefrom one bead to the other, each ply comprising cords arranged with thesame pitch and along the same direction, the cords of each ply beingstaggered with respect to those of the other by half the pitch, thecords of the two plies, in regions of the carcass close to the beads,being located respectively at different distances from the inner wall ofthe tire, and successive cords of each ply, in regions of the carcassbetween the midheights of the two sidewalls, being inserted betweenadjacent cords of the other ply, so that the cords of the two plies, insaid regions of the carcass between the midheights of the two sidewalls,are located substantially at the same distance from the inner wall ofthe tire.

2. A tire according to claim 1 wherein the cords lie in radial planes ofthe tire.

3. A tire according to claim 1 wherein the cords are made of a materialof high modulus of elasticity.

4. A tire according to claim 3 wherein the cords are made of steel.

5. A tire according to claim 1 comprising rubber, which forms bridgesbetween the cords, the width of the rubber bridges between adjacentcords at the shoulders being substantially equal to the width of therubber bridges between adjacent cords of either ply in the beads.

6. A tire according to claim 1 comprising rubber, which forms bridgesbetween the cords, the width of the rubber bridges between adjacentcords at the shoulders being between one-fourth and three-fourths thediameter of the cords.

7. A tire according to claim 1 comprising rubber, which forms bridgesbetween the cords, characterized in that, at all points of the carcass,the width of the rubber bridges between adjacent cords which are at thesame distance from the inner wall of the tire is within the range of avalue which is a fraction of a cord diameter to a value which slightlyexceeds a cord diameter.

1. A tire comprising an annular tread portion, a pair of sidewallsrespectively extending radially inwardly from opposite edges of thetread portion, a pair of shoulders respectively at the junctions of thetread portion and the sidewalls, a pair of beads respectively at theradially inner edges of the sidewalls, and a carcass formed of at leastone pair of plies adjacent to each other and extending through the tirefrom one bead to the other, each ply comprising cords arranged with thesame pitch and along the same direction, the cords of each ply beingstaggered with respect to those of the other by half the pitch, thecords of the two plies, in regions of the carcass close to the beads,being located respectively at different distances from the inner wall ofthe tire, and successive cords of each ply, in regions of the carcassbetween the midheights of the two sidewalls, being inserted betweenadjacent cords of the other ply, so that the cords of the two plies, insaid regions of the carcass between the midheights of the two sidewalls,are located substantially at the same distance from the inner wall ofthe tire.
 2. A Tire according to claim 1 wherein the cords lie in radialplanes of the tire.
 3. A tire according to claim 1 wherein the cords aremade of a material of high modulus of elasticity.
 4. A tire according toclaim 3 wherein the cords are made of steel.
 5. A tire according toclaim 1 comprising rubber, which forms bridges between the cords, thewidth of the rubber bridges between adjacent cords at the shouldersbeing substantially equal to the width of the rubber bridges betweenadjacent cords of either ply in the beads.
 6. A tire according to claim1 comprising rubber, which forms bridges between the cords, the width ofthe rubber bridges between adjacent cords at the shoulders being betweenone-fourth and three-fourths the diameter of the cords.
 7. A tireaccording to claim 1 comprising rubber, which forms bridges between thecords, characterized in that, at all points of the carcass, the width ofthe rubber bridges between adjacent cords which are at the same distancefrom the inner wall of the tire is within the range of a value which isa fraction of a cord diameter to a value which slightly exceeds a corddiameter.